Bug 1466968 [wpt PR 11360] - Reland "WaveShaper must output non-zero values even...

Bug 1466968 [wpt PR 11360] - Reland "WaveShaper must output non-zero values even if input is silent", a=testonly

Automatic update from web-platform-testsReland "WaveShaper must output non-zero values even if input is silent"

This is a reland of 325b492fe733ba4c8b2128069a0a232fea1789e3

Initialize tail_time_ in constructor so we don't have uninitialized
variable.

Original change's description:
> WaveShaper must output non-zero values even if input is silent
>
> If the curve for the WaveShaperNode is such that a zero input produces
> a non-zero output, the WaveShaperNode needs to output that value even
> if the input is silent (or disconnected).
>
> Do this by setting the tail time of the processor to 0 or infinity
> depending on whether the curve specifies an output value of zero or
> not, respectively.
>
> Bug: 807301
> Test: WaveShaper/silent-inputs.html
> Change-Id: I6539d2e00f5d3e624ffaf2810944eb6d53d6f84b
> Reviewed-on: https://chromium-review.googlesource.com/896266
> Commit-Queue: Raymond Toy <rtoy@chromium.org>
> Reviewed-by: Hongchan Choi <hongchan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#564186}

Bug: 807301
Change-Id: I866c5b303b40c1245d86daf43c592eed39d6a9c9
Reviewed-on: https://chromium-review.googlesource.com/1087427
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564630}

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wpt-commits: 57285cd910b61105ec3b6b8a49d8e875ff8dec69
wpt-pr: 11360